Picture coding device, picture coding method, and picture coding program, and picture decoding device, picture decoding method, and picture decoding program

ABSTRACT

In a picture coding device, a significant coefficient information coding controller  706  and an arithmetic encoder  701  code significant difference coefficient information indicating that a difference coefficient value is not zero and significant for each of the difference coefficients in the partial region of the coding target. A difference coefficient value coding controller  707  and the arithmetic encoder  701  code difference coefficient values when significant difference coefficient information is significant for each of pixels in the partial region of the coding target. The significant coefficient information coding controller  706  decides a context for coding the significant difference coefficient information in the partial region of the coding target based on information indicating significance of the difference coefficient in the coded partial region.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.15/498,098, filed Apr. 26, 2017, which is a Continuation of U.S. patentapplication Ser. No. 14/478,788, filed Sep. 5, 2014, now U.S. Pat. No.9,667,977, which is a Continuation of International Application No.PCT/JP2013/002033, filed Mar. 26, 2013, which claims the benefit ofJapanese Patent Application Nos. 2012-069718 and 2012-069719, filed Mar.26, 2012, and 2013-062961 and 2013-062962, filed Mar. 25, 2013.

BACKGROUND 1. Field of the Invention

The present invention relates to picture coding and decoding technique,and more particularly, to entropy coding and decoding techniques ofresidual signals.

In MPEG-4 AVC as an international standard for moving picture coding,context-adaptive binary arithmetic coding called CABAC is employed as anentropy coding scheme. In the CABAC, a plurality of variables called acontext for storing a probability of occurrence of information to becoded are used. An optimal context is selected from neighboring codinginformation and used for coding. Since a probability of occurrence isupdated by a coding process in each context, it is possible to estimatea probability of occurrence of coding information with a high degree ofaccuracy and perform efficient coding.

RELATED ART LIST Patent Document

Patent Literature 1: JP 2007-300517 A

In MPEG-4 AVC, as a context is switched based on decoded neighboringinformation, learning of a probability of occurrence based on a decodingresult is performed in addition to estimation of a probability ofoccurrence of information. It is possible to optimize a probability ofoccurrence of information to be decoded for each context, and thuscoding efficiency is improved. However, it is necessary to sequentiallyprocess a calculation of a context index and decoding of significantdifference coefficient information for all significant differencecoefficient information in a processing target block, and thus it takesa time to calculate.

Patent Literature 1 discloses a technique of arranging a context for asyntax element having a high frequency of occurrence on a memory havingsmall access latency and reducing a processing delay related todecoding. However, the technique disclosed in Patent Literature 1 doesnot solve dependence of a calculation of a context index and decoding asyntax element and is not an essential solution to a processing delaysince it is difficult to perform the calculation and the decoding inparallel.

SUMMARY

The present invention was made in light of the foregoing, and it is anobject of the present invention to provide picture coding and decodingtechniques that are capable of performing parallel processing and thusimplementing a context index calculating method having a smallcomputation amount in difference coefficient coding/decoding and thatare simple in a circuit configuration and suitable for real-timeprocessing. It is another object of the present invention to providepicture coding and decoding techniques capable of implementing highcoding efficiency by calculating a context index with reference to aneighboring difference coefficient that is appropriate in terms of acorrelation.

A picture coding device according to one embodiment of the presentinvention is a picture coding device that partitions differenceinformation between a picture serving as a coding target and a pictureserving as a prediction target into a plurality of sub blocks, and codesthe partitioned sub block in a certain order, the picture coding deviceincludes: a significant sub block information encoder (706, 708, 701)that codes significant sub block information indicating whether or notall values of difference coefficients belonging to the sub block arezero; a significant difference coefficient information encoder (706,708) that codes significant difference coefficient informationindicating whether or not the value of the difference coefficient iszero; a difference coefficient value encoder (707, 701) that codes thevalue of the difference coefficient; and a context deriver (707, 701)that derives a context for coding the significant difference coefficientinformation of the sub block serving as the coding target based on atleast one of the significant sub block information, the significantdifference coefficient information, and the value of the differencecoefficient of the coded sub block neighboring the sub block serving asthe coding target.

Another embodiment of the present invention provides a picture codingmethod. This method is a picture coding method of partitioningdifference information between a picture serving as a coding target anda picture serving as a prediction target into a plurality of sub blocks,and codes the partitioned sub block in a certain order, and includes:coding significant sub block information indicating whether or not allvalues of difference coefficients belonging to the sub block are zero;coding significant difference coefficient information indicating whetheror not the value of the difference coefficient is zero; coding the valueof the difference coefficient; and deriving a context for coding thesignificant difference coefficient information of the sub block servingas the coding target based on at least one of the significant sub blockinformation, the significant difference coefficient information, and thevalue of the difference coefficient of the coded sub block neighboringthe sub block serving as the coding target.

Further, another embodiment of the present invention provides atransmitting device. This device includes: a packet processor thatpacketizes a bitstream coded by a picture coding method of partitioningdifference information between a picture serving as a coding target anda picture serving as a prediction target into a plurality of sub blocks,and codes the partitioned sub block in a certain order, and obtaincoding data; and a transmitter that transmits the packetized codingdata. The picture coding method includes: coding significant sub blockinformation indicating whether or not all values of differencecoefficients belonging to the sub block are zero; coding significantdifference coefficient information indicating whether or not the valueof the difference coefficient is zero; coding the value of thedifference coefficient; and deriving a context for coding thesignificant difference coefficient information of the sub block servingas the coding target based on at least one of the significant sub blockinformation, the significant difference coefficient information, and thevalue of the difference coefficient of the coded sub block neighboringthe sub block serving as the coding target.

Further, another embodiment of the present invention provides atransmission method. This method includes: packetizing a bitstream codedby a picture coding method of partitioning difference informationbetween a picture serving as a coding target and a picture serving as aprediction target into a plurality of sub blocks, and codes thepartitioned sub block in a certain order, and obtaining coding data; andtransmitting the packetized coding data. The picture coding methodincludes: coding significant sub block information indicating whether ornot all values of difference coefficients belonging to the sub block arezero; coding significant difference coefficient information indicatingwhether or not the value of the difference coefficient is zero; codingthe value of the difference coefficient; and deriving a context forcoding the significant difference coefficient information of the subblock serving as the coding target based on at least one of thesignificant sub block information, the significant differencecoefficient information, and the value of the difference coefficient ofthe coded sub block neighboring the sub block serving as the codingtarget.

A picture decoding device according an embodiment of the presentinvention is a picture decoding device that decodes a bitstream obtainedby partitioning difference information between a picture serving as adecoding target and a picture serving as a prediction target into aplurality of sub blocks and coding the partitioned sub block in acertain order, and includes: a significant sub block information decoder(1006, 1008, 1001) that decodes significant sub block informationindicating whether or not all values of difference coefficientsbelonging to the sub block are zero; a significant differencecoefficient information decoder (1006, 1008) that decodes significantdifference coefficient information indicating whether or not the valueof the difference coefficient is zero; a difference coefficient valuedecoder (1007, 1001) that decodes the value of the differencecoefficient; and a context deriver (1007, 1001) that derives a contextfor decoding the significant difference coefficient information of thesub block serving as the decoding target based on at least one of thesignificant sub block information, the significant differencecoefficient information, and the value of the difference coefficient ofthe decoded sub block neighboring the sub block serving as the decodingtarget.

Another embodiment of the present invention provides a picture decodingmethod. This method is a picture decoding method that decodes abitstream obtained by partitioning difference information between apicture serving as a decoding target and a picture serving as aprediction target into a plurality of sub blocks and coding thepartitioned sub block in a certain order, and includes: decodingsignificant sub block information indicating whether or not all valuesof difference coefficients belonging to the sub block are zero; decodingsignificant difference coefficient information indicating whether or notthe value of the difference coefficient is zero; decoding the value ofthe difference coefficient; and deriving a context for decoding thesignificant difference coefficient information of the sub block servingas the decoding target based on at least one of the significant subblock information, the significant difference coefficient information,and the value of the difference coefficient of the decoded sub blockneighboring the sub block serving as the decoding target.

Further, another embodiment of the present invention provides areceiving device. This device is a receiving device that receives abitstream obtained by coding a moving picture and decodes the receivedbitstream, and includes: a receiver that receives coding data obtainedby packetizing a bitstream obtained by partitioning differenceinformation between a picture serving as a decoding target and a pictureserving as a prediction target into a plurality of sub blocks and codingthe partitioned sub block in a certain order; a reconstructor thatperforms packet processing on the received packetized coding data toreconstruct the bitstream; a significant sub block information decoder(1006, 1008, 1001) that decodes significant sub block informationindicating whether or not all values of difference coefficientsbelonging to the sub block are zero from the reconstructed bitstream; asignificant difference coefficient information decoder (1006, 1008) thatdecodes significant difference coefficient information indicatingwhether or not the value of the difference coefficient is zero from thereconstructed bitstream; a difference coefficient value decoder (1007,1001) that decodes the value of the difference coefficient from thereconstructed bitstream; and a context deriver (1007, 1001) that derivesa context for decoding the significant difference coefficientinformation of the sub block serving as the decoding target based on atleast one of the significant sub block information, the significantdifference coefficient information, and the value of the differencecoefficient of the decoded sub block neighboring the sub block servingas the decoding target.

Further, another embodiment of the present invention provides areception method. This method is a reception method of receiving abitstream obtained by coding a moving picture and decoding the receivedbitstream, and includes: receiving coding data obtained by packetizing abitstream obtained by partitioning difference information between apicture serving as a decoding target and a picture serving as aprediction target into a plurality of sub blocks and coding thepartitioned sub block in a certain order; performing packet processingon the received packetized coding data to reconstruct the bitstream;decoding significant sub block information indicating whether or not allvalues of difference coefficients belonging to the sub block are zerofrom the reconstructed bitstream; decoding significant differencecoefficient information indicating whether or not the value of thedifference coefficient is zero from the reconstructed bitstream;decoding the value of the difference coefficient from the reconstructedbit stream, and deriving a context for decoding the significantdifference coefficient information of the sub block serving as thedecoding target based on at least one of the significant sub blockinformation, the significant difference coefficient information, and thevalue of the difference coefficient of the decoded sub block neighboringthe sub block serving as the decoding target.

Further, an embodiment obtained by exchanging an arbitrary combinationof the above components and an expression of the present invention amonga method, a device, a system, a recording medium, a computer program,and the like is also effective as an aspect of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described, byway of example only, with referenceto the accompanying drawings which are meant to be exemplary, notlimiting, and wherein like elements are numbered alike in severalFigures, in which:

FIG. 1 is a flowchart for describing a difference coefficient decodingprocess according to a related art;

FIG. 2 is a flowchart for describing a sub block difference coefficientdecoding process according to a related art;

FIG. 3 is a flowchart for describing a significant differencecoefficient decoding process according to a related art;

FIG. 4 is a flowchart for describing a difference coefficient valuedecoding process according to a first embodiment;

FIG. 5 is a block diagram illustrating a configuration of a picturecoding device that performs a difference coefficient coding methodaccording to an embodiment;

FIG. 6 is a block diagram illustrating a configuration of a picturedecoding device that performs a difference coefficient decoding methodaccording to the embodiment;

FIG. 7 is a diagram for describing a scan order of differencecoefficients of a sub block;

FIG. 8 is a block diagram illustrating a detailed configuration of thepicture decoding device of FIG. 6 according to the first embodiment;

FIG. 9 is a diagram for describing a definition of a neighboringdifference coefficient in the significant difference coefficientdecoding process of FIG. 3;

FIG. 10 is a diagram for describing a definition of a neighboringdifference coefficient in a significant difference coefficient decodingprocess of FIG. 13;

FIG. 11 is a diagram for describing a definition of a context in thesignificant difference coefficient decoding process of FIG. 4;

FIG. 12 is a diagram for describing sub block partitioning of adifference coefficient;

FIG. 13 is a flowchart for describing a difference coefficient valuedecoding process according to the first embodiment;

FIG. 14 is a diagram for describing a coding block size;

FIG. 15 is a block diagram illustrating a detailed configuration of thepicture coding device of FIG. 5 according to the first embodiment;

FIG. 16 is a flowchart for describing a difference coefficient codingprocess according to the first embodiment;

FIG. 17 is a flowchart for describing a sub block difference coefficientcoding process according to the first embodiment;

FIG. 18 is a flowchart for describing a significant differencecoefficient coding process according to the first embodiment;

FIG. 19 is a flowchart for describing a difference coefficient valuecoding process according to the first embodiment; and

FIG. 20 is a diagram for describing a configuration of using a sub blockposition for a calculation of a context of significant differencecoefficient information.

DETAILED DESCRIPTION

The invention will now be described by reference to the preferredembodiments. This does not intend to limit the scope of the presentinvention, but to exemplify the invention.

A technique as the premise of an embodiment of the present inventionwill be first described.

A technique of associating each coding syntax with a plurality ofcontexts and selecting a context based on a correlation of a syntaxelement can optimize code allocation and thus can be efficient coding.

As exemplary context adaptive entropy coding, a process of decoding aquantization orthogonal transform coefficient of a difference signal tobe coded in a 16×16 size will be described with reference to a flowchartof FIG. 1. FIG. 12 illustrates a quantization orthogonal transformcoefficient of a processing target. Hereinafter, a quantizationorthogonal transform coefficient is referred to as a “differencecoefficient.” In the present process, a 16×16 difference coefficient ofa processing target is partitioned into sub blocks 401 to 416 of a 4×4size, and scanning is preferentially performed in units of sub blocks.

A sub block of a processing target is decided according to a scan orderthat will be described later (S101). When scanning of all sub blocksends, a difference coefficient decoding process ends. A referencenumeral 902 in FIG. 7 indicates a sub block scan order. In the presentprocess, scanning starts from a lower rightmost sub block in adifference coefficient region, is performed according to a rule in whichit proceeds from the under right to the upper left and then from theunder right to the upper left, and ends at a upper leftmost sub block. Areference numeral 901 in FIG. 7 is a diagram illustrating a sub blockscan order using arrows. When scanning is performed according to thescan order of FIG. 7, it becomes a state in which scanning of sub blockspositioned at spatially right and lower sides among all processingtarget sub blocks is completed.

Referring back to the flowchart of FIG. 1, a process of decoding alldifference coefficient values of the processing target sub block isperformed (S102). After the sub block difference coefficient values aredecoded, the process proceeds to step S101.

The details of the sub block difference coefficient value decodingprocess will be described with reference to the flowchart of FIG. 2.

Significant sub block information is decoded (S201). The significant subblock information is a 1-bit flag indicating that there is a non-zerodifference coefficient in the processing target sub block. Thesignificant sub block information of 1 indicates that there is at leastone non-zero difference coefficient in the processing target sub block.The significant sub block information of 0 indicates that all differencecoefficients of the processing target sub block are 0.

A value of the significant sub block information is determined (S202).When the significant sub block information is 0, all the differencecoefficient values of the processing target sub block are set to 0(S209), and then the sub block difference coefficient value decodingprocess ends.

When the significant sub block information is 1, a process of decodingall significant difference coefficient information of the processingtarget sub block is performed (S203). The significant differencecoefficient information is a 1-bit flag indicating that a differencecoefficient value at a processing target position is not 0. Thesignificant coefficient information of 1 indicates that a differencecoefficient value at a processing target position is not 0, and thesignificant coefficient information of 0 indicates that a differencecoefficient value at a processing target position is 0. The details ofthe process of decoding the significant difference coefficientinformation of the sub block will be described later. After allsignificant difference coefficient information of the sub block isdecoded, the process proceeds to decoding of a difference coefficientvalue of step S204.

A difference coefficient value decoding process is performed (S204). Thedetails of the difference coefficient value decoding process will bedescribed later. The difference coefficient value decoding process iscompleted, the process proceeds to step S101, and scanning of a next subblock is performed.

[Significant Difference Coefficient Information Decoding Process]

The process of decoding the significant difference coefficientinformation of the sub block in step S203 will be described withreference to a flowchart of FIG. 3.

A processing target sub block is decided according to a certain scanorder (S301). The scan order of difference coefficients in a sub blockis assumed to follow the rule illustrated in FIG. 7, similarly to thesub block scan order in the difference coefficient region.

A neighboring significant difference coefficient sum countCoeff that isa sum of the number of non-zero difference coefficients that neighbor aprocessing target difference coefficient position and are decoded iscalculated (S302). FIG. 9 illustrates an exemplary differencecoefficient position for calculating the neighboring significantdifference coefficient sum countCoeff. A reference numeral 202 indicatesneighboring difference coefficients when a processing target position isa reference numeral 201, and a reference numeral 204 indicatesneighboring difference coefficients when a processing target position isa reference numeral 203. As illustrated in FIG. 9, five differencecoefficients that are positioned at the right and lower sides of theprocessing target difference coefficient position and neighboring theprocessing target difference coefficient position are assumed to beneighboring difference coefficients. Since the scan order of thedifference coefficients follows the rule of FIG. 7, differencecoefficients that belong to the same sub block as the processing targetdifference coefficient and are positioned at the right and lower sidesof the processing target difference coefficient position are decodedcoefficients. Similarly, significant difference coefficients belongingto sub blocks at the right and lower sides of the sub block positionedat the processing target position are decoded coefficients. Theneighboring difference coefficient sum countCoeff is a variable forestimating a probability of occurrence of a significant differencecoefficient. Due to characteristics and visual characteristics of apicture, significant difference coefficients are likely to beconcentrated on “1” at a low frequency range and “0” at a high frequencyrange. Since a significant difference coefficient has a spatialcorrelation, a difference coefficient neighboring the processing targetposition is set as a calculation target for the neighboring differencecoefficient sum countCoeff. Neighboring difference coefficientsindicating the outside of the difference coefficient region are excludedfrom a calculation for the neighboring significant coefficient sumcountCoeff.

Referring back to the flowchart of FIG. 3, it is determined whether ornot the neighboring significant coefficient sum countCoeff is 0 (S303).When the neighboring significant coefficient sum countCoeff is 0, acontext index ctxIdx for decoding the significant difference coefficientinformation is set to 0 (S304), and the significant differencecoefficient information is decoded using a context corresponding to thecontext index ctxIdx. Then, the significant difference coefficientinformation is set as the difference coefficient value (S308).

When the neighboring significant coefficient sum countCoeff is not 0,determines whether or not the neighboring significant coefficient sumcountCoeff is smaller than or equal to 2 (S305). When the neighboringsignificant coefficient sum countCoeff is smaller than or equal to 2,the context index ctxIdx for decoding the significant differencecoefficient information is set to 1 (S306), and the significantdifference coefficient information is decoded using the contextcorresponding to the context index ctxIdx. Then, the significantdifference coefficient information is set as the difference coefficientvalue (S308).

When the neighboring significant coefficient sum countCoeff is neithersmaller than nor equal to 2, that is, when the neighboring significantcoefficient sum countCoeff is larger than or equal to 3, the contextindex ctxIdx for decoding the significant difference coefficientinformation is set to 2 (S307), and the significant differencecoefficient information is decoded using the context corresponding tothe context index ctxIdx. Then, the significant difference coefficientinformation is set as the difference coefficient value (S308).

A context is a variable for storing a probability of occurrence ofinformation to be decoded, and allocation of a code word is switchedbased on a probability of occurrence indicated by a context. In theabove example, three contexts for coding a significant differencecoefficient are defined, and a context for decoding a significantdifference coefficient is decided based on the magnitude of theneighboring significant difference coefficient sum. In advance, a highprobability of occurrence of the significant coefficient information of0 is set to a context corresponding to the context index ctxIdx (=0)when the neighboring significant coefficient sum countCoeff is 0, and ahigh probability of occurrence of the significant coefficientinformation of 1 is set to a context corresponding to the context indexctxIdx (=2) when the neighboring significant coefficient sum countCoeffis larger than or equal to 3. Since it is possible to reduce a codingamount for information having a high probability of occurrence, thecoding efficiency can be improved by increasing the estimation accuracyof the probability of occurrence.

In MPEG-4 AVC, learning of a probability of occurrence based on adecoding result is performed in addition to estimation of a probabilityof occurrence of information by switching of a context based on decodedneighboring information. It is possible to optimize a probability ofoccurrence of information to be decoded for each context, and thus thecoding efficiency is improved.

Commonly, information of an orthogonal transform component of a pictureis likely to be concentrated at a low frequency range. Further, sincevisual characteristics have little influence on degradation of a highfrequency component, coarse quantization of a high frequency componentis often practically performed. Thus, the significant coefficientinformation tends to be concentrated on the low frequency component. Thesignificant coefficient information has a high correlation with theneighboring significant coefficient, it is logical in terms of codingefficiency to switch a context based on the number of neighboringsignificant coefficient information.

[Difference Coefficient Value Decoding Process]

The process of decoding difference coefficient values of a sub block instep S204 in the flowchart of FIG. 2 will be described with reference toa flowchart of FIG. 13.

A processing target sub block is decided according to a certain scanorder (S501). The scan order of difference coefficients in the sub blockis assumed to follow the rule illustrated in FIG. 7, similarly to thescan order of the significant difference coefficient information. Whenscanning of all the difference coefficients of the sub block ends, theprocess of decoding the difference coefficient value is completed, andthe process proceeds to a process of deciding a next sub block (S101).

It is determined whether or not the difference coefficient value at theprocessing target difference coefficient position is 0 (S502). When thedifference coefficient value at the processing target differencecoefficient position is 0, decoding of the difference coefficient valueat the processing target difference coefficient position is completed,and the process proceeds to step S501.

When the difference coefficient value at the processing targetdifference coefficient position is 1, the absolute value of thedifference coefficient at the processing target difference coefficientposition is decoded (S503). When the present process is performed, thedifference coefficient value is decided to be not 0, code wordsaccording to values obtained by subtracting 1 from the absolute valuesof the difference coefficients are coded. Thus, a value obtained byadding 1 to a value obtained by entropy-decoding a code word is set asthe absolute value of the difference coefficient.

A sign of the difference coefficient at the processing target differencecoefficient position is decoded (S504). The difference coefficient valueis decided based on the absolute value of the difference coefficient andthe sign of the difference coefficient.

In the significant difference coefficient information decoding process,201 in FIG. 9 is scanned lastly in the sub block as indicated by thescan order of 902 in FIG. 7, and its scan order is 16 as indicated in902 in FIG. 7. Further, among difference coefficients 202 neighboring201, the scan order of a position neighboring below 201 is 15, and it isscanned directly before 201. Since the context index ctxIdx necessaryfor decoding the significant difference coefficient information of 201is decoded based on the sum of the significant difference coefficientsof 202, it is difficult to decide the context index ctxIdx of 201 untilthe decoding of the significant difference coefficient information of202 is completed. It means that it is necessary to sequentially processa calculation of ctxIdx and decoding the significant differencecoefficient information for all significant difference coefficientinformation in the sub block, and thus it is difficult to reduce timecomplexity by parallelization. Meanwhile, an occupancy ratio of thedifference coefficient on a bitstream is high, and the context indexcalculation process and the decoding process of the significantdifference coefficient information are large in their occupied timecomplexity in the entire decoding process. In other words, the decodingprocess of the significant coefficient information hits a maximumbottleneck in the real-time decoding process.

Patent Literature 1 discloses a technique of arranging a context for asyntax element having a high frequency of occurrence on a memory havingsmall access latency and reducing a processing delay related todecoding. However, the technique disclosed in Patent Literature 1 doesnot solve dependence on calculation of a context index and decoding asyntax element and is not an essential solution to a processing delaysince it is difficult to perform the calculation and the decoding inparallel.

In this regard, according to an embodiment of the present invention,provided are picture coding and decoding techniques that are capable ofeliminating dependence between a calculation of a context index andcoding/decoding of significant difference coefficient information,performing parallel processing and implementing a context indexcalculating method having a small computation amount in differencecoefficient coding/decoding and that are simple in a circuitconfiguration and suitable for real-time processing. Further, providedare picture coding and decoding techniques capable of implementing highcoding efficiency by calculating a context index with reference to aneighboring difference coefficient that is appropriate in terms of acorrelation. Hereinafter, an embodiment of the present invention will bedescribed.

In the following description, a “processing target block” refers to acoding target block in the case of a coding process performed by apicture coding device, and refers to a decoding target block in the caseof a decoding process performed by a picture decoding device. A“processed block” refers to a coded block in the case of a codingprocess performed by a picture coding device, and refers to a decodedblock in the case of a decoding process performed by a picture decodingdevice. Hereinafter, these meanings are used unless otherwise described.

[Coding Device]

An exemplary picture coding device according to the present inventionwill be described with reference to the appended drawings. FIG. 5 is ablock diagram illustrating a configuration of a picture coding deviceaccording to an embodiment. The picture coding device according to theembodiment includes a subtractor 501, an orthogonaltransformer/quantizer 502, an inverse quantizer/inverse transformer 503,an adder 504, a decoded picture memory 505, a predictor 506, adifference information encoder 507, a prediction information encoder508, and a mode determiner 509.

The mode determiner 509 tries to code all prediction candidate, anddecides optimal prediction information for each block of pictures. Theprediction information includes a partition block size, a predictionmode indicating inter prediction/intra prediction are included, motioninformation such as a motion vector and a reference picture index whenthe prediction mode is the inter prediction, and an intra predictionmode when the prediction mode is the intra prediction. The decidedprediction information is supplied to the predictor 506 and theprediction information encoder 508.

The prediction information encoder 508 performs variable length codingon the input prediction information, and outputs a bitstream of theprediction information.

The predictor 506 constructs a prediction picture using the inputprediction information and a decoded picture stored in the decodedpicture memory 505, and supplies the constructed prediction picture tothe subtractor 501.

The subtractor 501 constructs a difference picture by subtracting theprediction picture from the original picture of the coding target, andsupplies the constructed difference signal to the orthogonaltransformer/quantizer 502.

The orthogonal transformer/quantizer 502 performs orthogonal transformand quantization on the difference picture to construct a differencecoefficient, and supplies the constructed difference coefficient to theinverse quantizer/inverse transformer 503 and the difference informationencoder 507.

The difference information encoder 507 performs entropy coding on thedifference coefficient, and outputs the bitstream sequence of thedifference information.

The inverse quantizer/inverse transformer 503 performs inversequantization and inverse orthogonal transform on the differencecoefficient received from the orthogonal transformer/quantizer 502 toconstruct a decoded difference signal, and supplies the constructeddecoded difference signal to the adder 504.

The adder 504 adds the prediction picture to the decoded differencesignal to construct a decoded picture, and causes the constructeddecoded picture to be stored in the decoded picture memory 505.

[Decoding Device]

An exemplary picture decoding device according to the present inventionwill be described with reference to the appended drawings. FIG. 6 is ablock diagram illustrating a configuration of a moving picture decodingdevice according to an embodiment. The picture decoding device accordingto the embodiment includes a difference information decoder 801, aninverse quantizer/inverse transformer 802, a prediction informationdecoder 803, an adder 804, a decoded picture memory 805, and a predictor806.

Since the decoding process of the picture decoding device of FIG. 6corresponds to the decoding process provided in the picture codingdevice of FIG. 5, the respective components of the inversequantizer/inverse transformer 802, the adder 804, the decoded picturememory 805, and the predictor 806 of FIG. 8 have functions correspondingto the respective components of the inverse quantizer/inversetransformer 503, the adder 504, the decoded picture memory 505, and thepredictor 506 of the picture coding device of FIG. 5.

The prediction information decoder 803 performs entropy decoding on theinput prediction information bitstream to construct predictioninformation, and supplies the constructed prediction information to thepredictor 806.

The predictor 806 constructs a prediction picture using the inputprediction information and a decoded picture stored in the decodedpicture memory 805, and supplies the constructed prediction picture tothe adder 804.

The difference information decoder 801 performs entropy decoding on thedifference information to construct difference information. Theconstructed difference information is supplied to the inversequantizer/inverse transformer 802.

The inverse quantizer/inverse transformer 802 performs inversequantization and inverse orthogonal transform on the differenceinformation received from the difference information decoder 801 toconstruct the decoded difference signal, and supplies the constructeddecoded difference signal to the adder 804.

The adder 804 adds the prediction picture to the decoded differencesignal to construct a decoded picture, and outputs the constructeddecoded picture to be stored in the decoded picture memory 805.

The difference coefficient coding and decoding processes according tothe embodiment of the present invention are performed in the differenceinformation encoder 507 of the moving picture coding device of FIG. 5and the difference information decoder 801 of the moving the picturedecoding device of FIG. 8. Next, the details of the differenceinformation coding and decoding processes according to an embodimentwill be described.

[Coding Block]

In the embodiment, as illustrated in FIG. 14, a screen is hierarchicallypartitioned into rectangular blocks, and a sequential process based on acertain processing order is performed on the respective blocks. Eachpartitioned block is referred to as a “coding block.” A block 1817 ofFIG. 14 is a maximum unit of partition in an embodiment, and referred toas a maximum coding block. A block 1816 of FIG. 14 is a minimum unit ofpartition in an embodiment, and referred to as a minimum coding block.Hereinafter, the minimum coding block and the maximum coding block willbe described as 4×4 pixels and 16×16 pixels.

[Prediction Block]

Among coding blocks, a unit in which intra prediction is performed isreferred to as a prediction block. A prediction block has a size that islarger than or equal to the minimum coding block and smaller than orequal to the maximum coding block. In FIG. 14, blocks 1802, 1803, and1804 are 16×16 blocks, blocks 1805, 1810, 1811, and 1801 are 8×8 blocks,and blocks 1806, 1807, 1808, and 1809 are 4×4 blocks. Blocks 1812, 1813,1814, and 1815 are non-processed blocks, and coding block sizes thereofare not decided yet. In the coding process, an optimal prediction blocksize is decided, and a prediction block size is coded. In the decodingprocess, a prediction block size is derived from a bitstream. Thefollowing description will proceed in connection with an example inwhich a prediction block is used as a processing unit.

[Processing Unit of Difference Coefficient]

A unit in which quantization and orthogonal transform are performed isidentical to a unit of a prediction block, but in the coding/decodingprocess, it is assumed that a difference coefficient region ispartitioned into a plurality of sub blocks, and scanning is performed.The size of a sub block is assumed to be a 4×4 size. FIG. 12 illustratesa difference coefficient region of a 16×16 size. 401 to 416 are subblocks. Here, a unit in which quantization and orthogonal transform areperformed may be decided independently of a unit of a prediction block.

First Embodiment

[Coding Process]

A first embodiment of a difference information coding method accordingto an embodiment of the present invention will be described. FIG. 15 isa block diagram illustrating a detailed configuration of the differenceinformation encoder 507 of FIG. 5 according to the first embodiment. Thedifference information encoder 507 according to the first embodimentincludes an arithmetic encoder 701, a difference coefficient buffer 702,a coding controller 703, a context memory 704, and a scan controller705, and the coding controller 703 includes a significant coefficientinformation coding controller 706, a difference coefficient value codingcontroller 707, and a significant sub block information codingcontroller 708.

Next, the difference coefficient coding process will be described withreference to flowcharts of FIGS. 16, 17, 18, and 19.

The scan controller 705 decides a processing target sub block (S601).When scanning of all sub blocks is completed, the difference coefficientdecoding process ends. 902 in FIG. 7 indicates a sub block scan order.In the present process, scanning starts from a lower rightmost sub blockin a difference coefficient region, is performed according to a rule ofproceeding from the under right to the upper left and then from theunder right to the upper left, and ends at a upper leftmost sub block. Acontext is updated through a coding process as described above. When thescan order is applied, there is a processing advantage of improving anestimation accuracy of a probability of occurrence of a differencecoefficient of a frequency component by performing coding of a lowfrequency component in which a difference coefficient is likely to occurafter coding of a high frequency component. A reference numeral 901 ofFIG. 7 is a diagram illustrating a sub block scan order using arrows.When scanning is performed according to the scan order of FIG. 7, itbecomes a state in which scanning of sub blocks positioned at spatiallyright and lower sides among processing target sub blocks is completed. Asub block coding process is performed on the processing target sub block(S602).

[Sub Block Coding Process (S602)]

The significant sub block information coding controller 708 derives aprocessing target sub block from the difference coefficient buffer 702.When all difference coefficients of the sub block are scanned and allthe difference coefficient values are 0, the significant sub blockinformation is set to 0. Otherwise (when there is at least one non-zerothe difference coefficient value), the significant sub block informationis set to 1 (S701).

The significant sub block information coding controller 708 decides thecontext index ctxIdx for coding the significant sub block informationwith reference to the difference coefficients included in a decoded subblock neighboring the processing target sub block from the differencecoefficient buffer 702. The context corresponding to the context indexctxIdx is read out from the context memory 704. The significant subblock information and the context are transferred to the arithmeticencoder 701. The arithmetic encoder 701 codes the significant sub blockinformation using the context (S702).

The significant sub block information coding controller 708 determines avalue of the significant sub block information (S703). When thesignificant sub block information is 0, the sub block differencecoefficient value coding process ends, and then the process proceeds tostep S601.

When the significant sub block information is 1, a process of coding allsignificant difference coefficient information of the processing targetsub block is performed (S704). The details of the process of coding thesignificant difference coefficient information will be described later.After coding of all significant difference coefficient information ofthe sub block ends, the process proceeds to coding of a differencecoefficient value of step S704.

The difference coefficient value coding controller 707 performs aprocess of coding all difference coefficient values of the processingtarget sub block (S705). The details of the process of coding thedifference coefficient value of the sub block will be described later.After coding all the difference coefficient values of the sub blockends, the process proceeds to step S601.

[Significant Difference Coefficient Information Coding Process (S704)]

The significant coefficient information coding controller 706 calculatesthe sum of the number of non-zero difference coefficients neighboringthe processing target sub block, that is, the neighboring significantcoefficient sumcountCoeff (S801). In the present process, differencecoefficients that belong to sub blocks positioned at spatially right andlower sides of the processing target sub block and are neighboring theprocessing target sub block are defined as neighboring differencecoefficients.

FIG. 10 illustrates a neighboring difference coefficient position. Areference numeral 301 indicates a processing target sub block, and areference numeral 302 indicates a neighboring difference coefficient. Aneighboring difference coefficient indicating the outside of thedifference coefficient region is excluded from a calculation of theneighboring significant coefficient sum countCoeff. Differencecoefficients 303 belonging to sub blocks at the right and lower sides ofthe processing target sub block can have any of a configuration includedin the neighboring difference coefficient and a configuration notincluded in the neighboring difference coefficient. In the configurationin which the reference numeral 303 is included in the neighboringdifference coefficient, the number of neighboring differencecoefficients increases, and thus a probability of occurrence of thesignificant difference coefficient information can be estimated with ahigh degree of accuracy. In the configuration in which the referencenumeral 303 is not included in the neighboring difference coefficient, acomputation amount and a circuit size can be reduced due to a reductionin an addition process related to the neighboring significantcoefficient sum countCoeff and a reduction in a process of determiningthe boundary of the difference coefficient region.

The significant coefficient information coding controller 706 decidesthe difference coefficients of the processing target (S802). The scanorder of the difference coefficients in the sub block is assumed tofollow the rule illustrated in FIG. 7, similarly to the sub block scanorder in the difference coefficient region. When scanning of allsignificant difference coefficients of the sub block ends, thesignificant difference coefficient coding process ends, and then theprocess proceeds to the difference coefficient value coding process(S704).

The significant coefficient information coding controller 706 determineswhether or not the neighboring significant coefficient sum countCoeff is0 (S803).

When the neighboring significant coefficient sum countCoeff is 0, theprocessing target difference coefficient position in the processingtarget sub block is determined (S804). A horizontal-direction differencecoefficient position is assumed to be posX, a vertical-directiondifference coefficient position is assumed to be posY, and theprocessing target difference coefficient position is assumed to bepos=posX+posY. When pos<=2, the context index ctxIdx for coding thesignificant coefficient information is set to 1 (S805), and otherwise(pos>2), the context index ctxIdx is set to 0 (S806). A referencenumeral 601 of FIG. 11 indicates a definition of the context indexctxIdx when countCoeff=0.

When the neighboring significant coefficient sum countCoeff is not 0, itis determined whether or not the neighboring significant coefficient sumcountCoeff is smaller than or equal to 1 (S807). When the neighboringsignificant coefficient sum countCoeff is smaller than or equal to 1,the processing target difference coefficient position in the processingtarget sub block is determined (S808). When pos<=3, the context indexctxIdx for decoding the significant coefficient information is set to 1(S809), and otherwise (pos>3), the context index ctxIdx is set to 0(S810). A reference numeral 602 of FIG. 11 indicates a definition of thecontext index ctxIdx when countCoeff=1.

When the neighboring significant coefficient sum countCoeff is neithersmaller than nor equal to 1, it is determined whether or not theneighboring significant coefficient sum countCoeff is smaller than orequal to 2 (S811). When the neighboring significant coefficient sumcountCoeff is smaller than or equal to 2, the processing targetdifference coefficient position in the processing target sub block isdetermines (S812). When pos<=2, the context index ctxIdx for decodingthe significant coefficient information is set to 2 (S813), andotherwise (pos>2), the context index ctxIdx is set to 1 (S814). Areference numeral 603 of FIG. 11 indicates a definition of the contextindex ctxIdx when countCoeff=2.

When the neighboring significant coefficient sum countCoeff is neithersmaller than nor equal to 2, the context index ctxIdx for decoding thesignificant coefficient information is set to 2 (S815). A referencenumeral 605 of FIG. 11 indicates a definition of the context indexctxIdx when countCoeff>2.

The significant coefficient information coding controller 706 derivesthe difference coefficient of the processing target position from thedifference coefficient buffer 702. When the difference coefficient valueis not 0, the significant difference coefficient information is set to1, and otherwise (when the difference coefficient value is 0), thesignificant difference coefficient information is set to 0 (S816).

The significant coefficient information coding controller 706 reads acontext corresponding to the decided context index ctxIdx from thecontext memory 704, and transfers the significant difference coefficientinformation and the context to the arithmetic encoder 701. Thearithmetic encoder 701 codes the significant difference coefficientinformation using the context (S817).

[Difference Coefficient Value Coding Process (S705)]

The difference coefficient value coding controller 707 decides thedifference coefficients of the processing target (S901). The scan orderof the difference coefficients in the sub block is assumed to follow therule illustrated in FIG. 7, similarly to the scan order of thesignificant difference coefficients. When scanning of all differencecoefficients of the sub block ends, the difference coefficient valuecoding process ends, and the process proceeds to a process of deciding anext sub block (S601).

The difference coefficient value coding controller 707 determineswhether or not the difference coefficient value at the processing targetdifference coefficient position is 0 (S902). When the differencecoefficient value at the processing target difference coefficientposition is 0, coding of the difference coefficient value at theprocessing target difference coefficient position is completed, and theprocess proceeds to step S901.

When the difference coefficient value at the processing targetdifference coefficient position is not 0, the absolute value of thecoding difference coefficient at the processing target differencecoefficient position and a sign are calculated (S903 and S904). When thepresent process is performed, since the difference coefficient value isdecided to be not 0, the coding difference coefficient absolute value isa value obtained by subtracting 1 from the absolute value of thedifference coefficient. Further, when the difference coefficient ispositive, the sign is set to 0, and when the difference coefficient isnegative, the sign is set to 1.

The difference coefficient value coding controller 707 reads a contextfrom the context memory 704, and transfers the coding absolute value andthe context to the arithmetic encoder 701. The arithmetic encoder 701decides the coding absolute value using the context (S905).

The difference coefficient value coding controller 707 reads a contextfrom the context memory 704, and transfers the coding absolute value andthe context to the arithmetic encoder 701. The arithmetic encoder 701decides the coding absolute value using the context (S905).

[Decoding Process]

A first embodiment of a difference coefficient decoding method accordingto an embodiment of the present will be described. FIG. 8 is a blockdiagram illustrating a detailed configuration of the differenceinformation decoder 801 of FIG. 6 according to the first embodiment. Thedifference information decoder 801 according to the first embodimentincludes an arithmetic decoder 1001, a difference coefficient buffer1002, a decoding controller 1003, a context memory 1004, and a scancontroller 1005, and the decoding controller 1003 includes a significantcoefficient information decoding controller 1006, a differencecoefficient value decoding controller 1007, and a significant sub blockinformation decoding controller 1008.

Since the difference information decoding process in the differenceinformation decoder 801 of FIG. 8 corresponds to the differenceinformation coding process in the difference information encoder 507 ofFIG. 5, the respective components of the difference coefficient buffer1002, the context memory 1004, and the scan controller 1005 in thedifference information decoder of FIG. 8 have functions corresponding tothe respective components of the difference coefficient buffer 702, thecontext memory 704, and the scan controller 705 of FIG. 15.

Next, the difference information decoding process will be described withreference to the flowcharts of FIGS. 1, 2, 4, and 13.

The scan controller 1005 decides a processing target sub block (S101).When scanning of all sub blocks ends, the difference coefficientdecoding process ends. 902 in FIG. 7 indicates a sub block scan order.In the present process, scanning starts from a lower rightmost sub blockin a difference coefficient region, is performed according to a rule ofproceeding from the under right to the upper left and then from theunder right to the upper left, and ends at a upper leftmost sub block.901 in FIG. 7 is a diagram illustrating a sub block scan order usingarrows. When scanning is performed according to the scan order of FIG.7, it becomes a state in which scanning of sub blocks positioned atspatially right and lower sides among processing target sub blocks iscompleted. The sub block decoding process is performed on the processingtarget sub block (S102).

[Sub Block Decoding (S102)]

The significant sub block information decoding controller 1008 decides acontext for decoding the significant sub block information withreference to difference coefficients included in a coded sub blockneighboring the processing target sub block from the differencecoefficient buffer 1002, and reads the decided context from the contextmemory 1004. The context and a decoding command are transferred to thearithmetic decoder 1001. The arithmetic decoder 1001 performs abitstream decoding process using the context, and decodes thesignificant sub block information (S201).

The significant sub block information decoding controller 1008determines a value of the significant sub block information (S202). Whenthe significant sub block information is 0, all the differencecoefficient values of the processing target sub block of the differencecoefficient buffer 1002 are set to 0 (S209), and the sub blockdifference coefficient value decoding process ends.

When the significant sub block information is 1, the decoding process isperformed on all significant difference coefficient information of theprocessing target sub block (S203). The details of the sub blocksignificant difference coefficient information decoding process will bedescribed later. After the decoding of all significant differencecoefficient information of the sub block ends, the process proceeds todecoding of the difference coefficient value of step S204.

The decoding process of all the difference coefficient values of theprocessing target sub block is performed (S204). The details of the subblock difference coefficient value decoding process will be describedlater. After the decoding of all the difference coefficient values ofthe sub block ends, the process proceeds to step S101.

[Significant Difference Coefficient Information Decoding Process (S203)]

The significant coefficient information decoding controller 1006calculates the sum countCoeff of the number of significant differencecoefficients neighboring the processing target difference coefficientposition (S401). In the present process, difference coefficientsbelonging to sub blocks positioned at spatially right and lower sides ofthe processing target sub block and neighboring the processing targetsub block are defined as neighboring difference coefficients.

FIG. 10 illustrates a neighboring difference coefficient position. Areference numeral 301 indicates a processing target sub block, and areference numeral 302 indicates a neighboring difference coefficient. Aneighboring difference coefficient indicating the outside of thedifference coefficient region is excluded from a calculation of theneighboring significant coefficient sum countCoeff. Differencecoefficients 303 belonging to sub blocks at the right and lower sides ofthe processing target sub block can have any of a configuration includedin the neighboring difference coefficient and a configuration notincluded in the neighboring difference coefficient. In the configurationin which the reference numeral 303 is included in the neighboringdifference coefficient, the number of neighboring differencecoefficients increases, and thus a probability of occurrence of thesignificant difference coefficient information can be estimated with ahigh degree of accuracy. In the configuration in which the referencenumeral 303 is not included in the neighboring difference coefficient, acomputation amount and a circuit size can be reduced due to a reductionin an addition process related to the neighboring significantcoefficient sum countCoeff and a reduction in a process of determiningthe boundary of the difference coefficient region.

The significant coefficient information decoding controller 1006 decidesthe difference coefficients of the processing target (S402). The scanorder of the difference coefficients in the sub block is assumed tofollow the rule illustrated in FIG. 7, similarly to the sub block scanorder in the difference coefficient region. When scanning of allsignificant difference coefficients of the sub block ends, thesignificant difference coefficient decoding process is completed, andthen the process proceeds to the difference coefficient value decodingprocess (S204). The significant coefficient information decodingcontroller 1006 determines whether or not the neighboring significantcoefficient sum countCoeff is 0 (S403). When the neighboring significantcoefficient sum countCoeff is 0, the processing target differencecoefficient position in the processing target sub block is determined(S404). A horizontal-direction difference coefficient position isassumed to be posX, a vertical-direction difference coefficient positionis assumed to be posY, and the processing target difference coefficientposition is assumed to be pos=posX+posY. When pos<=2, the context ctxIdxfor decoding the significant coefficient information is set to 1 (S405),and otherwise (pos>2), the context ctxIdx is set to 0 (S406). Areference numeral 601 of FIG. 11 indicates a definition of the contextwhen countCoeff=0. After the decided context is read from the contextmemory 1004, the context and the decoding command are transferred to thearithmetic decoder 1001. The arithmetic decoder 1001 performs thebitstream decoding process using the context, and decodes thesignificant difference coefficient information (S416).

When the neighboring significant coefficient sum countCoeff is not 0, itis determined whether or not the neighboring significant coefficient sumcountCoeff is smaller than or equal to 1 (S407). When the neighboringsignificant coefficient sum countCoeff is smaller than or equal to 1,the processing target difference coefficient position in the processingtarget sub block is determined (S408). When pos<=3, the context indexctxIdx for decoding the significant coefficient information is set to 1(S409), and otherwise (pos>3), the context index ctxIdx is set to 0(S410). A reference numeral 602 of FIG. 11 indicates a definition of thecontext when countCoeff=1. After the decided context is read from thecontext memory 1004, the context and the decoding command aretransferred to the arithmetic decoder 1001. The arithmetic decoder 1001performs the bitstream decoding process using the context, and decodesthe significant difference coefficient information (S416).

When the neighboring significant coefficient sum countCoeff is neithersmaller than nor equal to 1, it is determined whether or not theneighboring significant coefficient sum countCoeff is smaller than orequal to 2 (S411). When the neighboring significant coefficient sumcountCoeff is smaller than or equal to 2, the processing targetdifference coefficient position in the processing target sub block isdetermined (S412). When pos<=2, the context index ctxIdx for decodingthe significant coefficient information is set to 2 (S413), andotherwise (pos>2), the context index ctxIdx is set to 1 (S414). Areference numeral 603 of FIG. 11 indicates a definition of the contextwhen countCoeff=2. After the decided context is read from the contextmemory 1004, the context and the decoding command are transferred to thearithmetic decoder 1001. The arithmetic decoder 1001 performs thebitstream decoding process using the context, and decodes thesignificant difference coefficient information (S416).

When the neighboring significant coefficient sum countCoeff is neithersmaller than nor equal to 2, the context index ctxIdx for decoding thesignificant coefficient information is set to 2 (S415). A referencenumeral 605 of FIG. 11 indicates a definition of the context whencountCoeff>2. After the decided context is read from the context memory1004, the context and the decoding command are transferred to thearithmetic decoder 1001. The arithmetic decoder 1001 performs thebitstream decoding process using the context, and decodes thesignificant difference coefficient information (S416).

When the neighboring significant coefficient sum countCoeff is large,all significant coefficient information in the processing target subblock is likely to be 1. Thus, in the above process, when theneighboring significant coefficient sum countCoeff is larger than orequal to 3, ctxIdx is set to 2 regardless of the value of pos. Further,it is also possible to break down the determination condition of theneighboring significant coefficient sum countCoeff. For example, in thecase in which the neighboring significant coefficient sum countCoeff islarger than or equal to 3, the context index definition of the referencenumeral 604 of FIG. 11 can be used when the neighboring significantcoefficient sum countCoeff is 3, and the context index definition of thereference numeral 605 of FIG. 11 can be used when the neighboringsignificant coefficient sum countCoeff is larger than or equal to 4.Through this configuration, it is possible to improve neighboringinformation correlation use efficiency and coding efficiency.

In the present process, the sum of the number of significant coefficientinformation of decoded neighboring sub blocks and the position of aprocessing target difference coefficient in a sub block are referred toin calculating the context index ctxIdx for the significant differencecoefficient information. The reason of using this configuration isdescribed below.

Commonly, orthogonal transform coefficients of a picture are likely tobe concentrated on low frequency components, and the significantcoefficient information is likely to be 1. Further, since the highfrequency component of the orthogonal transform coefficient is hardlyvisually affected and often coarsely quantized, the coefficient value ofthe high frequency component becomes 0, and the significant coefficientinformation of the high frequency component is likely to be 0. Thisfeature is not limited to the entire difference coefficient region andsimilarly applies to each sub block without, and the significantcoefficient information of components of a sub block at a low frequencyrange side is more likely to be 1 than that of components of the samesub block at a high frequency range side. When the value of the contextindex ctxIdx of the significant difference coefficient information atthe low frequency range in the sub block is set to be larger than thevalue of the context index ctxIdx of the significant differencecoefficient information at the high frequency range, the estimationaccuracy of the probability of occurrence of the significant coefficientinformation is improved. Further, in the high frequency range in whichthe significant difference coefficient is likely to be 0, theneighboring significant coefficient sum is also small, and in the lowfrequency range in which the significant difference coefficient islikely to be 1, the neighboring significant coefficient sum stronglytends to be large, and when the neighboring significant coefficient sumis used as an index indicating how much the target sub block includesthe significant difference coefficient information, the estimationaccuracy of the probability of occurrence of the significant coefficientinformation is improved.

In the present process, it is possible to calculate the context indicesof all coefficient positions in the sub block by calculating theneighboring significant difference coefficient sum for the sub blockonly once. Compared to the method of individually calculating theneighboring significant difference coefficient sum at each coefficientposition, it is possible to reduce the computation amount of theneighboring significant difference coefficient sum. Further, in theconfiguration of using a decoding result of an immediately previoussignificant difference coefficient in the scan order for a calculationof the context index, it is necessary to sequentially perform acalculation of the context index in the sub block and decoding of thesignificant difference coefficient. In the present embodiment, theneighboring significant difference coefficient sum and the processingtarget coefficient position are referred to for a calculation of thecontext index, but since the difference coefficients belonging to theprocessing target sub block are not used for the neighboring significantdifference coefficient sum, there is no dependence relation between subblocks in the calculation of the context index. Since it is possible tocalculate the context indices for all the significant differencecoefficients at the beginning of the sub block, it is possible toperform the calculation of the context index and the decoding process ofthe significant difference coefficient information in parallel. It ispossible to reduce the processing delay related to decoding of thesignificant coefficient information that is high in the frequency ofoccurrence in the bitstream.

Instead of referring to the neighboring significant coefficient, it ispossible to calculate the context with reference to the significant subblock information. In other words, it is possible to calculate thecontext based on the sum of neighboring significant sub blockinformation other than the sum of neighboring significant coefficients.For example, a configuration of using the sum of significant sub blockinformation of a neighboring sub block at the right side of a processingtarget sub block and significant sub block information of a neighboringsub block at the lower side of the processing target sub block canreduce the computation amount and the circuit size compared to theabove-described configuration. Further, it is possible to use a subblock position for a context calculation. As described above, there is afeature in which the low frequency component is higher in theprobability of occurrence of the significant coefficient than the highfrequency range. As the sub block position is used for the contextcalculation, high-accuracy context estimation can be implemented. FIG.20 illustrates an example in which the difference coefficient region isdivided into two regions of a low frequency region and a high frequencyregion. In FIG. 20, reference numerals 1101, 1102, 1103, 1104, 1105, and1109 indicate low frequency components, and reference numerals 1106,1107, 1108, 1110, 1111, 1112, 1113, 1114, 1115, and 1116 indicate highfrequency regions. A configuration of calculating the context indexctxIdx in the above-described process for the high frequency region andthen adding an offset according to a certain sub block position to thecontext index ctxIdx for the low frequency region may be used, and aconfiguration of adding conditional branching to a sub block positionwhile calculating the context index ctxIdx for the low frequency regionmay be used. Further, a configuration of calculating the context indexctxIdx in the above-described process for the low frequency region andthen consistently set the context ctxIdx=0 for the high frequency regionsince the significant difference coefficient is usually likely to be 0,and the number of neighboring significant difference coefficients islikely to have a probability estimation error may be used.

Further, it is possible to calculate the context index the sum ofneighboring coefficient absolute values using the neighboringcoefficient absolute values instead of the neighboring significantdifference coefficient sum. Since the difference coefficient absolutevalue of the low frequency component is commonly large, when the sum ofneighboring difference coefficient absolute values is large, it ispossible to improve the coding efficiency by setting the context so thatthe probability of occurrence of the significant difference coefficientinformation is high.

Furthermore, it is possible to improve the context estimation accuracyby adding the prediction mode used to calculate the differencecoefficient to a condition determination in the process of calculatingthe context index of the significant difference coefficient. It isbecause of a feature difference in which commonly, compared to the intraprediction in which only a decoded region of a decoding target pictureis used as a reference target, the inter prediction in which it ispossible to refer to a plurality of decoded pictures is high in theprediction accuracy and a difference hardly occurs.

[Difference Coefficient Value Decoding Process (S204)]

The significant coefficient information decoding controller 1006 decidesthe difference coefficients of the processing target (S501). The scanorder of the difference coefficients in the sub block is assumed tofollow the rule illustrated in FIG. 7, similarly to the scan order ofthe significant difference coefficients. When scanning of all differencecoefficients of the sub block ends, the difference coefficient valuedecoding process is completed, and the process proceeds to a process ofdeciding a next sub block (S101).

The significant coefficient information decoding controller 1006determines whether or not the difference coefficient value at theprocessing target difference coefficient position is 0 (S502). When thedifference coefficient value at the processing target differencecoefficient position is 0, decoding of the difference coefficient valueat the processing target difference coefficient position is completed,and the process proceeds to step S501.

When the difference coefficient value at the processing targetdifference coefficient position is 1, the absolute value of thedifference coefficient at the processing target difference coefficientposition is decoded (S503). When the present process is performed, thedifference coefficient value is decided to be not 0, and code wordsaccording to values obtained by subtracting 1 from the absolute valuesof the difference coefficients are decoded as a bitstream. Thus, a valueobtained by adding 1 to a value obtained by entropy-decoding a code wordis set as the absolute value of the difference coefficient.

The sign of the difference coefficient at the processing targetdifference coefficient position is decoded (S504). The differencecoefficient value is decided based on the absolute value of thedifference coefficient and the sign of the difference coefficient.

In the present embodiment, the context index for decoding thesignificant difference coefficient information is calculated based onthe significant difference coefficient information of the decoded subblock, but a similar process can be applied to a calculation of thecontext index of the difference coefficient value. Since the differencecoefficient value has a correlation with the neighboring coefficientvalue and has a feature of being concentrated on the low frequencycomponent similarly to the significant difference coefficientinformation, the difference coefficient value can be efficiently codedby setting a context index indicating that a probability of occurrenceof a large difference coefficient value is high when the neighboringsignificant difference coefficient sum or the neighboring differencecoefficient absolute value sum is large and setting a context indexindicating that a probability of occurrence of a small differencecoefficient value is high when the neighboring significant differencecoefficient sum or the neighboring difference coefficient absolute valuesum is small.

The picture coding device and the picture decoding device according tothe first embodiment have the following effects.

(1) It is possible to calculate a context index of a processing targetdifference coefficient based on difference coefficients belonging to adecoded sub block neighboring a sub block to which the processing targetdifference coefficient belongs. It is possible to set an appropriateprobability model based on a neighboring correlation of significantdifference coefficient information by setting a context estimating thata probability of occurrence of significant difference coefficientinformation 1 is high when a neighboring significant differencecoefficient sum is large and that a probability of occurrence ofsignificant difference coefficient information 0 is high when aneighboring significant difference coefficient sum is small.Accordingly, it is possible to efficiently code significant differencecoefficient information.

(2) A context index is calculated based on a position of a processingtarget difference coefficient in a sub block. A context is set toestimate that difference coefficients at a low frequency range in a subblock are higher in a probability of occurrence of a significantdifference coefficient 1 than difference coefficients at a highfrequency range in a sub block. It is possible to set an appropriateprobability model based on a feature of significant differencecoefficient information on a frequency region, and it is possible toefficiently code significant difference coefficient information.

(3) A calculation of a neighboring significant difference coefficientsum and a position of a processing target difference coefficient in asub block do not depend on a decoding result of significant differencecoefficient information in a sub block. Thus, since it is possible toprovide a configuration of processing a calculation of a context indexin a sub block and decoding of significant difference coefficientinformation in parallel, it is possible to reduce a processing delayrelated to a decoding process of significant difference coefficientinformation. It is possible to implement a decoding device that is anoccupancy ratio of difference coefficients on a bitstream, large in thenumber of processing, and suitable for real-time processing as aprocessing delay of significant difference coefficient information isreduced. Further, in a coding device, similarly, it is possible toreduce a processing delay of significant difference coefficientinformation coding.

(4) A single calculation has only to be performed in a sub block since acalculation result based on a neighboring significant differencecoefficient sum related to a calculation of a context index ofsignificant difference coefficient information, that is, the sum ofsignificant sub block information, significant difference coefficientinformation, or difference coefficient absolute values does not dependon a position of a processing target difference coefficient. It ispossible to reduce a computation amount related to a context indexcalculation compared to a configuration of calculating an individualneighboring significant difference coefficient sum according to aprocessing target difference coefficient position.

A bitstream of a picture output from the picture coding device accordingto the embodiment has a specific data format that can be decodedaccording to a coding technique used in the embodiment, and the picturedecoding device corresponding to the picture coding device can decodethe bitstream of the specific data format.

In order to exchange a bitstream between the picture coding device andthe picture decoding device, when a wired or wireless network is used, abitstream may be converted to have a data format suitable for atransmission form of a transmission path and then transmitted. In thiscase, a picture transmitting device that converts the bitstream outputfrom the picture coding device into coding data of the data formatsuitable for the transmission form of the communication path and thentransmits the coding data to the network and a picture receiving devicethat receives the coding data from the network, reconstructs thebitstream, and supplies the bitstream to the picture decoding device areprovided.

The picture transmitting device includes a memory that buffers thebitstream output from the picture coding device, a packet processor thatpacketizes the bitstream, and a transmitter that transmits thepacketized coding data via the network. The picture receiving deviceincludes a receiver that receives the packetized coding data via thenetwork, a memory that buffers the received coding data, and a packetprocessor that performs packet processing on the coding data, constructsthe bitstream, and supplies the bitstream to the picture decodingdevice.

Further, the process related to the coding and the decoding can beimplemented as a transmitting, accumulating, or receiving device usinghardware and can be implemented by firmware stored in read only memory(ROM), flash memory, or the like or computer software or the like. Thefirmware program and the software program can be recorded in a computerreadable recording medium and provided, can be provided from a servervia a wired or wireless network, or can be provided as data broadcastingof a terrestrial or satellite digital broadcasting.

The exemplary embodiments of the present invention have been describedso far. The embodiment is an example, and it should be understood bythose skilled in the art that the combination of the respectivecomponents or the respective processing processes can be variouslymodified, and various modifications can also be within the scope of thepresent invention.

[Item 1] A picture coding device that partitions difference informationbetween a picture serving as a coding target and a picture serving as aprediction target into a plurality of sub blocks, and codes thepartitioned sub block in a certain order, the picture coding devicecomprising:

a significant sub block information encoder that codes significant subblock information indicating whether or not all values of differencecoefficients belonging to the sub block are zero;

a significant difference coefficient information encoder that codessignificant difference coefficient information indicating whether or notthe value of the difference coefficient is zero;

a difference coefficient value encoder that codes the value of thedifference coefficient; and

a context deriver that derives a context for coding the significantdifference coefficient information of the sub block serving as thecoding target based on at least one of the significant sub blockinformation, the significant difference coefficient information, and thevalue of the difference coefficient of the coded sub block neighboringthe sub block serving as the coding target.

[Item 2] The picture coding device according to Item 1,

wherein the context deriver derives an index based on at least one ofthe significant sub block information of the coded sub blocks thatneighbor the sub block serving as the coding target at right and lowersides of the sub block serving as the coding target, one or more of thesignificant difference coefficient information belonging to the codedsub blocks, and one or more of the values of the difference coefficientsbelonging to the coded sub blocks, and derives the context based on thederived index.

[Item 3] The picture coding device according to Item 2,

wherein the context deriver further derives the context based on aposition of the difference coefficient belonging to the sub blockserving as the coding target.

[Item 4] The picture coding device according to Item 2 or 3,

wherein the index is derived based on at least one of an additionformula using the significant sub block information, an addition formulausing each significant difference coefficient information, and anaddition formula using an absolute value of the difference coefficientfor the coded sub blocks that neighbor at the right and lower sides.

[Item 5] A picture coding method of partitioning difference informationbetween a picture serving as a coding target and a picture serving as aprediction target into a plurality of sub blocks, and codes thepartitioned sub block in a certain order, the picture coding methodcomprising:

coding significant sub block information indicating whether or not allvalues of difference coefficients belonging to the sub block are zero;

coding significant difference coefficient information indicating whetheror not the value of the difference coefficient is zero;

coding the value of the difference coefficient; and

deriving a context for coding the significant difference coefficientinformation of the sub block serving as the coding target based on atleast one of the significant sub block information, the significantdifference coefficient information, and the value of the differencecoefficient of the coded sub block neighboring the sub block serving asthe coding target.

[Item 6] The picture coding method according to Item 5,

wherein the context deriving includes deriving an index based on atleast one of the significant sub block information of the coded subblocks that neighbor the sub block serving as the coding target at rightand lower sides of the sub block serving as the coding target, one ormore of the significant difference coefficient information belonging tothe coded sub blocks, and one or more of the values of the differencecoefficients belonging to the coded sub blocks, and derives the contextbased on the derived index.

[Item 7] The picture coding method according to Item 6,

wherein the context deriving further includes deriving the context basedon a position of the difference coefficient belonging to the sub blockserving as the coding target.

[Item 8] The picture coding method according to Item 6 or 7,

wherein the index is derived based on at least one of an additionformula using the significant sub block information, an addition formulausing each significant difference coefficient information, and anaddition formula using an absolute value of the difference coefficientfor the coded sub blocks that neighbor at the right and lower sides.

[Item 9] A picture coding program embedded on a non-transitorycomputer-readable recording medium and partitioning differenceinformation between a picture serving as a coding target and a pictureserving as a prediction target into a plurality of sub blocks, and codesthe partitioned sub block in a certain order, the program comprising:

coding significant sub block information indicating whether or not allvalues of difference coefficients belonging to the sub block are zero;

coding significant difference coefficient information indicating whetheror not the value of the difference coefficient is zero;

coding the value of the difference coefficient; and

deriving a context for coding the significant difference coefficientinformation of the sub block serving as the coding target based on atleast one of the significant sub block information, the significantdifference coefficient information, and the value of the differencecoefficient of the coded sub block neighboring the sub block serving asthe coding target.

[Item 10] The picture coding program according to Item 9,

wherein the context deriving includes deriving an index based on atleast one of the significant sub block information of the coded subblocks that neighbor the sub block serving as the coding target at rightand lower sides of the sub block serving as the coding target, one ormore of the significant difference coefficient information belonging tothe coded sub blocks, and one or more of the values of the differencecoefficients belonging to the coded sub blocks, and derives the contextbased on the derived index.

[Item 11] The picture coding program according to Item 10,

wherein the context deriving further includes deriving the context basedon a position of the difference coefficient belonging to the sub blockserving as the coding target.

[Item 12] The picture coding program according to Item 10 or 11,

wherein the index is derived based on at least one of an additionformula using the significant sub block information, an addition formulausing each significant difference coefficient information, and anaddition formula using an absolute value of the difference coefficientfor the coded sub blocks that neighbor at the right and lower sides.

[Item 13] A transmitting device, comprising:

a packet processor that packetizes a bitstream coded by a picture codingmethod of partitioning difference information between a picture servingas a coding target and a picture serving as a prediction target into aplurality of sub blocks, and codes the partitioned sub block in acertain order, and obtain coding data; and

a transmitter that transmits the packetized coding data,

wherein the picture coding method includes

coding significant sub block information indicating whether or not allvalues of difference coefficients belonging to the sub block are zero,

coding significant difference coefficient information indicating whetheror not the value of the difference coefficient is zero,

coding the value of the difference coefficient, and

deriving a context for coding the significant difference coefficientinformation of the sub block serving as the coding target based on atleast one of the significant sub block information, the significantdifference coefficient information, and the value of the differencecoefficient of the coded sub block neighboring the sub block serving asthe coding target.

[Item 14] A transmission method, comprising:

packetizing a bitstream coded by a picture coding method of partitioningdifference information between a picture serving as a coding target anda picture serving as a prediction target into a plurality of sub blocks,and codes the partitioned sub block in a certain order, and obtainingcoding data; and

transmitting the packetized coding data,

wherein the picture coding method includes

coding significant sub block information indicating whether or not allvalues of difference coefficients belonging to the sub block are zero,

coding significant difference coefficient information indicating whetheror not the value of the difference coefficient is zero,

coding the value of the difference coefficient, and

deriving a context for coding the significant difference coefficientinformation of the sub block serving as the coding target based on atleast one of the significant sub block information, the significantdifference coefficient information, and the value of the differencecoefficient of the coded sub block neighboring the sub block serving asthe coding target.

[Item 15] A transmission program embedded on a non-transitorycomputer-readable recording medium, comprising:

packetizing a bitstream coded by a picture coding method of partitioningdifference information between a picture serving as a coding target anda picture serving as a prediction target into a plurality of sub blocks,and codes the partitioned sub block in a certain order, and obtainingcoding data; and

transmitting the packetized coding data,

wherein the picture coding method includes

coding significant sub block information indicating whether or not allvalues of difference coefficients belonging to the sub block are zero,

coding significant difference coefficient information indicating whetheror not the value of the difference coefficient is zero,

coding the value of the difference coefficient, and

deriving a context for coding the significant difference coefficientinformation of the sub block serving as the coding target based on atleast one of the significant sub block information, the significantdifference coefficient information, and the value of the differencecoefficient of the coded sub block neighboring the sub block serving asthe coding target.

[Item 16] A picture decoding device that decodes a bitstream obtained bypartitioning difference information between a picture serving as adecoding target and a picture serving as a prediction target into aplurality of sub blocks and coding the partitioned sub block in acertain order, the picture decoding device comprising:

a significant sub block information decoder that decodes significant subblock information indicating whether or not all values of differencecoefficients belonging to the sub block are zero;

a significant difference coefficient information decoder that decodessignificant difference coefficient information indicating whether or notthe value of the difference coefficient is zero;

a difference coefficient value decoder that decodes the value of thedifference coefficient; and

a context deriver that derives a context for decoding the significantdifference coefficient information of the sub block serving as thedecoding target based on at least one of the significant sub blockinformation, the significant difference coefficient information, and thevalue of the difference coefficient of the decoded sub block neighboringthe sub block serving as the decoding target.

[Item 17] The picture decoding device according to Item 16,

wherein the context deriver derives an index based on at least one ofthe significant sub block information of the decoded sub blocks thatneighbor the sub block serving as the decoding target at right and lowersides of the sub block serving as the decoding target, one or more ofthe significant difference coefficient information belonging to thedecoded sub blocks, and one or more of the values of the differencecoefficients belonging to the decoded sub blocks, and derives thecontext based on the derived index.

[Item 18] The picture decoding device according to Item 17,

wherein the context deriver further derives the context based on aposition of the difference coefficient belonging to the sub blockserving as the decoding target.

[Item 19] The picture decoding device according to Item 17 or 18,

wherein the index is derived based on at least one of an additionformula using the significant sub block information, an addition formulausing each significant difference coefficient information, and anaddition formula using an absolute value of the difference coefficientfor the decoded sub blocks that neighbor at the right and lower sides.

[Item 20] A picture decoding method that decodes a bitstream obtained bypartitioning difference information between a picture serving as adecoding target and a picture serving as a prediction target into aplurality of sub blocks and coding the partitioned sub block in acertain order, the picture decoding method comprising:

decoding significant sub block information indicating whether or not allvalues of difference coefficients belonging to the sub block are zero;

decoding significant difference coefficient information indicatingwhether or not the value of the difference coefficient is zero;

decoding the value of the difference coefficient; and

deriving a context for decoding the significant difference coefficientinformation of the sub block serving as the decoding target based on atleast one of the significant sub block information, the significantdifference coefficient information, and the value of the differencecoefficient of the decoded sub block neighboring the sub block servingas the decoding target.

[Item 21] The picture decoding method according to Item 20,

wherein the context deriving includes deriving an index based on atleast one of the significant sub block information of the decoded subblocks that neighbor the sub block serving as the decoding target atright and lower sides of the sub block serving as the decoding target,one or more of the significant difference coefficient informationbelonging to the decoded sub blocks, and one or more of the values ofthe difference coefficients belonging to the decoded sub blocks, andderiving the context based on the derived index.

[Item 22] The picture decoding method according to Item 21,

wherein the context deriving further includes deriving the context basedon a position of the difference coefficient belonging to the sub blockserving as the decoding target.

[Item 23] The picture decoding method according to Item 21 or 22,

wherein the index is derived based on at least one of an additionformula using the significant sub block information, an addition formulausing each significant difference coefficient information, and anaddition formula using an absolute value of the difference coefficientfor the decoded sub blocks that neighbor at the right and lower sides.

[Item 24] A picture decoding program embedded on a non-transitorycomputer-readable recording medium and decoding a bitstream obtained bypartitioning difference information between a picture serving as adecoding target and a picture serving as a prediction target into aplurality of sub blocks and coding the partitioned sub block in acertain order, the program comprising:

decoding significant sub block information indicating whether or not allvalues of difference coefficients belonging to the sub block are zero;

decoding significant difference coefficient information indicatingwhether or not the value of the difference coefficient is zero;

decoding the value of the difference coefficient; and

deriving a context for decoding the significant difference coefficientinformation of the sub block serving as the decoding target based on atleast one of the significant sub block information, the significantdifference coefficient information, and the value of the differencecoefficient of the decoded sub block neighboring the sub block servingas the decoding target.

[Item 25] The picture decoding program according to Item 24,

wherein the context deriving includes deriving an index based on atleast one of the significant sub block information of the decoded subblocks that neighbor the sub block serving as the decoding target atright and lower sides of the sub block serving as the decoding target,one or more of the significant difference coefficient informationbelonging to the decoded sub blocks, and one or more of the values ofthe difference coefficients belonging to the decoded sub blocks, andderiving the context based on the derived index.

[Item 26] The picture decoding program according to Item 25,

wherein the context deriving further includes deriving the context basedon a position of the difference coefficient belonging to the sub blockserving as the decoding target.

[Item 27] The picture decoding program according to Item 25 or 26,

wherein the index is derived based on at least one of an additionformula using the significant sub block information, an addition formulausing each significant difference coefficient information, and anaddition formula using an absolute value of the difference coefficientfor the decoded sub blocks that neighbor at the right and lower sides.

[Item 28] A receiving device that receives a bitstream obtained bycoding a moving picture and decodes the received bitstream, comprising:

a receiver that receives coding data obtained by packetizing a bitstreamobtained by partitioning difference information between a pictureserving as a decoding target and a picture serving as a predictiontarget into a plurality of sub blocks and coding the partitioned subblock in a certain order;

a reconstructor that performs packet processing on the receivedpacketized coding data to reconstruct the bitstream;

a significant sub block information decoder that decodes significant subblock information indicating whether or not all values of differencecoefficients belonging to the sub block are zero from the reconstructedbitstream;

a significant difference coefficient information decoder that decodessignificant difference coefficient information indicating whether or notthe value of the difference coefficient is zero from the reconstructedbitstream;

a difference coefficient value decoder that decodes the value of thedifference coefficient from the reconstructed bitstream; and

a context deriver that derives a context for decoding the significantdifference coefficient information of the sub block serving as thedecoding target based on at least one of the significant sub blockinformation, the significant difference coefficient information, and thevalue of the difference coefficient of the decoded sub block neighboringthe sub block serving as the decoding target.

[Item 29] A reception method of receiving a bitstream obtained by codinga moving picture and decoding the received bitstream, comprising:

receiving coding data obtained by packetizing a bitstream obtained bypartitioning difference information between a picture serving as adecoding target and a picture serving as a prediction target into aplurality of sub blocks and coding the partitioned sub block in acertain order;

performing packet processing on the received packetized coding data toreconstruct the bitstream;

decoding significant sub block information indicating whether or not allvalues of difference coefficients belonging to the sub block are zerofrom the reconstructed bitstream;

decoding significant difference coefficient information indicatingwhether or not the value of the difference coefficient is zero from thereconstructed bitstream;

decoding the value of the difference coefficient from the reconstructedbitstream; and

deriving a context for decoding the significant difference coefficientinformation of the sub block serving as the decoding target based on atleast one of the significant sub block information, the significantdifference coefficient information, and the value of the differencecoefficient of the decoded sub block neighboring the sub block servingas the decoding target.

[Item 30] A reception program embedded on a non-transitorycomputer-readable recording medium and receiving a bitstream obtained bycoding a moving picture and decoding the received bitstream, the programcomprising:

receiving coding data obtained by packetizing a bitstream obtained bypartitioning difference information between a picture serving as adecoding target and a picture serving as a prediction target into aplurality of sub blocks and coding the partitioned sub block in acertain order;

performing packet processing on the received packetized coding data toreconstruct the bitstream;

decoding significant sub block information indicating whether or not allvalues of difference coefficients belonging to the sub block are zerofrom the reconstructed bitstream;

decoding significant difference coefficient information indicatingwhether or not the value of the difference coefficient is zero from thereconstructed bitstream;

decoding the value of the difference coefficient from the reconstructedbitstream; and

deriving a context for decoding the significant difference coefficientinformation of the sub block serving as the decoding target based on atleast one of the significant sub block information, the significantdifference coefficient information, and the value of the differencecoefficient of the decoded sub block neighboring the sub block servingas the decoding target.

What is claimed is:
 1. A picture decoding device that decodes abitstream obtained by partitioning difference information between apicture serving as a decoding target and a picture serving as aprediction target into a plurality of sub blocks and coding thepartitioned sub blocks in a certain order, the picture decoding devicecomprising: a significant sub block information decoder that decodessignificant sub block information indicating whether or not all valuesof difference coefficients belonging to a the sub block serving as adecoding target are zero; a significant difference coefficientinformation decoder that decodes significant difference coefficientinformation indicating whether or not the value of a the differencecoefficient is zero; a difference coefficient value decoder that decodesthe value of the difference coefficient; and a context deriver thatderives a context for decoding the significant difference coefficientinformation of difference coefficient serving as the decoding targetbased on sum of horizontal position and vertical position of thedifference coefficient in sub block serving as the decoding target, andat least one of (1) the significant sub block information of decoded subblocks neighboring to the sub block serving as the decoding target, (2)the significant difference coefficient information of differencecoefficients belonging to decoded sub blocks neighboring to the subblock serving as the decoding target, and or (3) values of differencecoefficients belonging to decoded sub blocks neighboring to the subblock serving as the decoding target, wherein, when a sum of ahorizontal-direction position and a vertical-direction position of thedifference coefficient serving as the decoding target is larger than asum of a horizontal-direction position and a vertical-direction positionof another difference coefficient belonging to the sub block serving asa decoding target, the context deriver derives a context having a valueequal to or smaller than a context for decoding said other differencecoefficient, and when a sum of a horizontal-direction position and avertical-direction position of the difference coefficient serving as thedecoding target is smaller than a sum of a horizontal-direction positionand a vertical-direction position of another difference coefficientbelonging to the sub block serving as a decoding target, the contextderiver derives a context having a value equal to or larger than acontext for decoding said other difference coefficient.
 2. A picturedecoding method that decodes a bitstream obtained by partitioningdifference information between a picture serving as a decoding targetand a picture serving as a prediction target into a plurality of subblocks and coding partitioned sub blocks in a certain order, the picturedecoding method comprising: decoding significant sub block informationindicating whether or not all values of difference coefficientsbelonging to a sub block serving as a decoding target are zero; decodingsignificant difference coefficient information indicating whether or notvalue of a difference coefficient is zero; decoding the value of thedifference coefficient; and deriving a context for decoding thesignificant difference coefficient information of difference coefficientserving as the decoding target based on sum of horizontal position andvertical position of the difference coefficient in sub block serving asthe decoding target, and at least one of (1) the significant sub blockinformation of decoded sub blocks neighboring to the sub block servingas the decoding target, (2) the significant difference coefficientinformation of difference coefficients belonging to decoded sub blocksneighboring to the sub block serving as the decoding target, and or (3)values of difference coefficients belonging to decoded sub blocksneighboring to the sub block serving as the decoding target, wherein,when a sum of a horizontal-direction position and a vertical-directionposition of the difference coefficient serving as the decoding target islarger than a sum of a horizontal-direction position and avertical-direction position of another difference coefficient belongingto the sub block serving as a decoding target, the deriving of a contextderives a context having a value equal to or smaller than a context fordecoding said other difference coefficient, and when a sum of ahorizontal-direction position and a vertical-direction position of thedifference coefficient serving as the decoding target is smaller than asum of a horizontal-direction position and a vertical-direction positionof another difference coefficient belonging to the sub block serving asa decoding target, the deriving of a context derives a context having avalue equal to or larger than a context for decoding said otherdifference coefficient.
 3. A non-transitory computer-readable recordingmedium having embodied thereon a picture decoding program decoding a bitstream obtained by partitioning difference information between a pictureserving as a decoding target and a picture serving as a predictiontarget into a plurality of sub blocks and coding partitioned sub blocksin a certain order, the program comprising: decoding significant subblock information indicating whether or not all values of differencecoefficients belonging to a sub block serving as a decoding target arezero; decoding significant difference coefficient information indicatingwhether or not value of a difference coefficient is zero; decoding thevalue of the difference coefficient; and deriving a context for decodingthe significant difference coefficient information of differencecoefficient serving as the decoding target based on sum of horizontalposition and vertical position of the difference coefficient in subblock serving as the decoding target, and at least one of (1) thesignificant sub block information of decoded sub blocks neighboring tothe sub block serving as the decoding target, (2) the significantdifference coefficient information of difference coefficients belongingto decoded sub blocks neighboring to the sub block serving as thedecoding target, and or (3) values of difference coefficients belongingto decoded sub blocks neighboring to the sub block serving as thedecoding target, wherein, when a sum of a horizontal-direction positionand a vertical-direction position of the difference coefficient servingas the decoding target is larger than a sum of a horizontal-directionposition and a vertical-direction position of another differencecoefficient belonging to the sub block serving as a decoding target, thederiving of a context derives a context having a value equal to orsmaller than a context for decoding said other difference coefficient,and when a sum of a horizontal-direction position and avertical-direction position of the difference coefficient serving as thedecoding target is smaller than a sum of a horizontal-direction positionand a vertical-direction position of another difference coefficientbelonging to the sub block serving as a decoding target, the deriving ofa context derives a context having a value equal to or larger than acontext for decoding said other difference coefficient.